Adjuvant palbociclib for ER+ breast cancer (PALLAS Trial (ABCSG-42/AFT-05/PrE0109/BIG-14-13): A preplanned analysis of the stage IIA cohort
Authors: Angela DeMichele, Amylou C. Dueck, Dominik Hlauschek, Miguel Martin, Harold J. Burstein, Georg Pfeiler, Nicholas Zdenkowski, Antonio C. Wolff, Marija Balic, Kathy Miller, David A. Cameron, Justin M. Balko, Tiffany A. Traina, Dorota Czajkowska, Otto Metzger, Dongrui Ray Lu, Patrick O'Brien, Christian Fesl, Erica L. Mayer, Michael Gnant
Journal: Journal of Clinical Oncology (2022)

390216 Background: CDK4/6 inhibitors have become standard of care for advanced hormone receptor positive, HER2-negative (HR+/HER2-) breast cancer in combination with endocrine therapy (ET), with one approved for high-risk patients (pts) in the adjuvant setting. The PALLAS Trial investigated the addition of palbociclib to adjuvant ET in pts with stage II-III breast cancer. Stage IIA patients were specifically enrolled to evaluate the potential benefit of using palbociclib with adjuvant ET pts diagnosed at lower risk who may have more indolent disease. Methods: In the prospective, randomized, phase III PALLAS trial, pts with HR+/HER2- early breast cancer were randomly assigned to receive adjuvant ET for at least 5 years with or without 2 years of palbociclib (125 mg orally once daily, days 1-21 of a 28-day cycle). ET was of provider’s choice. Stage IIA enrollment was capped at 1,000 patients. While the primary end point of the overall study was invasive disease-free survival (iDFS) for the entire cohort, there was a preplanned analysis of recurrence and survival endpoints in the stage IIA cohort. Outcomes were compared between arms using stratified log-rank tests and Cox models (stratification factors: chemotherapy and age ≤ 50). Results: Among 5,796 pts enrolled at 406 centers in 21 countries worldwide between 9/1/2015 and 11/30/2018, a total of 1,010 stage IIA pts were enrolled. The protocol-defined number of events occurred at a median follow-up of 50 months for this subgroup (43.1 months for the overall study). Median age within this subgroup was 54 (range 29-85 yrs), and 410 (40.6%) were pre/perimenopausal, 506 (50.1%) T2/N0 (vs T0-1/N1), 272 (26.9%) grade 3 (vs. grade1/2), and 561 (55.5%) received chemotherapy. iDFS events occurred in 31 of 503 (6.2%) pts who received palbociclib plus ET and in 45 of 507 (8.9%) pts who received ET alone, resulting in a statistically nonsignificant difference in iDFS at 4 years (92.9% vs. 92.1%; hazard ratio, 0.75; CI, 0.48 to 1.19; P = .23). Nonsignificant differences were also observed for invasive breast cancer-free, distant recurrence-free, and locoregional cancer-free survival. No significant differences in iDFS were observed in subgroups including age group, receipt of chemotherapy, tumor grade, and clinical risk (T1/N1 vs. T2/N0).Conclusions: In this preplanned analysis of the stage IIA cohort of the PALLAS trial, the addition of adjuvant palbociclib to standard ET did not improve outcomes over ET alone, suggesting no benefit from the agent in reducing the incidence of early relapse in pts with lower-stage HR+/HER2- breast cancer. Future analyses will incorporate genomic risk and other molecular patterns from the extensive transPALLAS correlative program. Additional follow-up (10-year minimum) is also underway to assess the impact of palbociclib exposure on late recurrence in HR+ disease. Clinical trial information: NCT02513394.